This invention relates to systems for carrying integrated circuit chips (IC), and more particularly to chip carriers.
In integrated circuit manufacture, a thin slice or wafer of semiconductor material is cut into individual circuits or chips. Each chip carries a set of bonding pads through which the chip must be connected to other chips and to the outside world. Each chip is then individually packaged. The package for the chip has package leads and a connection is made between each bonding pad of the chip and the corresponding package lead. Perhaps the most familiar chip package is the Dual In-Line Package or DIP in which a majority of integrated circuits are packaged in. Further external connections are then made between packaged leads, such as by ready-made connections on a printed circuit board upon which the individually packaged chips are mounted.
Another system used for connecting the bonding pads of chips to those of other chips or to the outside world is known as the chip carrier. A chip carrier is typically made of a substrate which is used as a base upon which is placed a sandwich-like structure composed of electrically insulating and conducting layers in an alternating arrangement to facilitate different types of electrical connections. The sandwich structure usually includes several layers of metal interconnect lines and power/ground planes sandwiched packaged. Instead the chips are turned upside down so that their bonding pads face downwards. In such a configuration, the chips are known as flip chips. The bonding pads are then connected to the sandwich structure through solder bumps. The solder bumps for a particular chip may be connected through via holes through one or more insulating layers of the structure to the desired interconnect lines or power/ground planes. In the introduction of U.S. Pat. No. 4,458,297, Stopper et al. there is a description of an interconnect structure of the type described above. The advantage of chip carriers over printed circuit boards is that the IC chips can be placed closer together on a chip carrier than on a printed circuit board.
As very large scale integration (VLSI) becomes more widely used om systems, VLSI circuit packages must be capable of handling large numbers of inputs and outputs and the packages must be capable of being cooled at an acceptable rate. In many systems it is desirable to use, in conjunction with the manufactured integrated circuit chips, certain circuit components such as resistors, capacitors, diodes and transistors for various functions. For very high speed computer applications, for example, electrical signal lines that exist between logic chips should be terminated in resistors. In conventional systems, resistors used for terminating the signal lines may form part of a larger chip; alternatively, a discrete resistor placed next to the chip may also be used. In either case the power dissipated by the resistor increases the amount of heat generated in the chip. The alternative of placing resistors next to the IC chip takes up valuable real estate. In VLSI circuits, a large number of chips are packed into a small area so that the amount of heat generated by the chips or in their vicinity is of critical concern. It is therefore desirable to provide a chip carrier which can be used to alleviate such difficulties.